Apparatus for producing a rotating time base display



.1. F. MCCOY 2,747,135

APPARATUS FOR PRODUCING A ROTATING TIME BASE DISPLAY 2 Sheets-Sheet lIN1/E NTOR. F.. M 'E E U Y .JUHN

ATTORNEY mw @L l MN may 22, 1956 Filed Aug. 28, 1953 J. F. MCCOY May 2z,1956 APPARATUS FOR PRODUCING A ROTATING TIME BASE DISPLAY Filed Aug.28,` 1953 2 Sheets-Shea?. 2

ATTORNEY United States Patent() APPARATUS FOR PRODUCING A ROTATINGTllVIE BASE DISPLAY John F. McCoy, Haddonfeld, N. J., assignor, by mesneassignments, to the United States of America as represented by theSecretary of the Navy Application August 2s, 1953, serial No. 377,096 7Claims. (Cl. 315-24) This invention relates generally to apparatus forproducing a rotating time base display on a cathode ray tube. Moreparticularly, the invention relates to apparatus for producing arotating time base display on a cathode ray tube, using a sine-cosinepotentiometer as a resolver. While neither specifically nor exclusivelylimited thereto, the apparatus of the present invention is particularlyuseful in radar apparatus of the type employing relatively slow moving,mechanical systems for indicating instantaneously and continuously theazimuth and the elevation of objects.

It has been proposed previously to use the sine-cosine potentiometer asa resolver in apparatus for producing a rotating time base display on acathode ray tube. Circuity for such apparatus is described in the bookCathode Ray Tube Displays, MIT Radiation Laboratory Series, volume 22,page 451, published by McGraw-Hill Book Company, Incorporated, New York,N. Y., 1948. This prior art apparatus uses two power supplies offsetwith respect to ground in order to produce a zero voltage across thesine-cosine potentiometer during the wait time. Each of the powersupplies provides operating potentials for a separate, associatedsaw-tooth generator. The output voltages of each saw-tooth generator areapplied to the ends of the sine-cosine potentiometer, respectively. Theresistor of the sine-cosine potentiometer is rotated and four brushesspaced 90 apart on a circle of rotation on the rotating resistor, takeofi four voltages, respectively, whose instantaneous peak amplitudesdepend on the instantaneous positions of the brushes on the rotatingresistor. Voltages from two pairs of alternate brushes are fed to thehorizontal and vertical deflection electrodes of a cathode ray tube. Theparticular construction of the sine-cosine potentiometer is alsodescribed on page 202 of the aforementioned book. v

It is a principal object of the present invention to provide improvedapparatus for producing a rotating time base display on a cathode raytube.

It is a further object of the present invention to provide improvedapparatus for producing a rotating time base display on a cathode raytube, that will require fewer components than the prior art apparatusfor accomplishing the same purpose.

It is still a further object of the present invention to provideimproved apparatus for producing a rotating time base display, for acathode ray tube, that may be used in radar apparatus employing lowfrequenecy saw-tooth waves and detlectioncircuits that have good lowfrequency responses.

Another object of the present invention is to provide improved apparatusfor producing a rotating time base display, on a cathode ray tube, whichis simple in construction, uses fewer components than prior artapparatus, and is highly efficient in use.

These and further objects of the present invention are attained inimproved apparatus using a sine-cosine potentiometer as a resolver, forproducing a rotating time base display on a cathode ray tube. Briey, theoutput ICC of a saw-tooth generator is applied to the input of aphase-splitter which may be a push-pull paraphase amplitier. The outputof the phase-splitter is fed push-pull to a pair of push-pull vcathodefollowers. The ends of a sine-cosine potentiometer are connected to thecathodes of the push-pull cathode followers, respectively. Each of apair of sliding contacts or brushes, spaced apart on the circle ofrotation of the sine-cosine potentiometer resistor, picks ofi voltageswhich vary from a maximum peak voltage of one polarity, through zero, toa maximum peak yvoltage of an opposite polarity. The voltages picked offby the brushes are fed to horizontal and vertical deilection amplifiers,respectfully. The output voltages of the deflection amplifiers are thenfed to the deection plates of the `cathode ray tube. The rotating timebase display on the cathode ray tube is thatof a trace in the form of adiameter of a circle on the face of the tube, revolving about itsmid-point. Should enough drive be available at the brushes of thesine-cosine potentiometer, the output voltages from four brushes couldthen be applied directly to the deflection plates of the cathode raytube, and the horizontal and vertical amplifiers could be eliminated. Inthe latter case, four brushes placed 90 apart with respect to the circleof rotation of the potentiometer resistance would be employed.

The novel features of the present invention, as well as the inventionitself, both as to its organization and method ot' operation, will beunderstood in detail from the following description when considered inconnection with the accompanying drawings in which Fig. l is a schematicdiagram partly in block diagram form, of apparatus for producing arotating time base display on a cathode ray tube, in accordance with theinvention; and Fig. 2 is a schematic diagram, partly in block diagramform, of av modified form of the invention illustrated in Fig. l.

Referring now to Fig. 1 of the drawings, there is shown apparatus forproducing a rotating time base display on the face of a cathode ray tube10. The apparatus comprises an alternating voltage generator, such as asaw-tooth generator 12, of conventional design, adapted to produce atits output a saw-tooth voltage, as shown by the waveform 14. Thesaw-tooth output voltage of the saw-tooth generator 12 may be of arelatively low frequency, say in the order of about 30 cycles persecond, as encountered in certain radar applications. The saw-toothoutput voltage of the saw-tooth generator 12 is applied to the input ofa phase-splitter 16 which may be of the push-pull paraphase amplifiertype. The out-v put saw-tooth voltage from the phase-splitter 16 isapplied in push-pull to the grids of two electron discharge devices,vacuum tubes 13 and 20, respectively, through output capacitors 22 and24, respectively. The anodes of the tubes 1S and 20 are connected toeach other, and to a source of operatingvoltage (not shown). The cathodeof the tube 18 is connected to ground through resistors 26 and 23; andthe cathode of the tube 20 is connected to ground through resistors 30and 32.

While the tubes 18 and 20 are shown as two separate tubes, it isunderstood that they may be a duotriode within a single envelope, suchas a type 5687 duotriode tube. The tubes 18 and 20 and their operatingpoints should be chosen to produce a high degree of linearity in theiroutput.

The resistor 26 should be equal to the resistance 30,

and the resistance 28 should be equal to the resistance 32.

lf conduction through the tubes 18 and 20, under these circumstances isnot equal, means well known in the art may be used to vary theseresistors so that conduction through the tubes 18 and 20 will beequalized. The grid of the tube 18 is connected to the junction of theresistors 26 and 28, through a grid leak resistor 34; and the grid 3 ofthe tube 20 is connected to the junction of the resistors 3U 'd 32,through grid leak resistor 36.

A sine-cosine potentiometer 38, of the type described in theaforementioned book, comprises a resistor 4t) in the form 'ofa wirewound Ion a 'square sheet of insulating material 42, such' as akelite.One end of the resistor 40 is connected to the cathode of the tube 1Sthrough a Contact brush 44 which rides on a ring 46, illustrated in partby a curved, dashed line, attached to one end of the resistor 40. Theother end of the resistor 4i) is connected to the cathode of the tube 20through a Contact brush 48y in sliding contact `with a ring 50,illustrated in part by a curved, *dashed line. The resistor 40 of thesinecosine potentiometer 3g is adapted to be rotated about an axisperpendicular to the'4 insulating material 42, at its center JS2.Brushes 54, 56,58 and 60 of the potentiomet`er138 are positioned 90 fromeach other on a circle of rotation 62. The circle of rotation 62represents bare portions of'L the wire of the resistor 46, and thebrushes 54, 56, 58 and 60 are in slideable contact therewith.

An important feature of the present invention is the D. C. voltageacross the resistor 4l) of the sine-cosine potentiometer 38 is zero atall times. It is this condition which permits the use of the circuit ofthe present invention with low frequency saw-tooth voltages and lowfrequency response deflection amplifiers. It is noted that if adifference of D. C. potential were to appear across the ends of resistor40,` the rotating time base display on the cathode ray tube wouldwobble.

In a preferred embodiment of the present invention, the output voltagesfrom the two brushes S4 and 56, spaced 90 apart on the circle ofrotation 62 of the sinecosine potentiometer 3S,- are fed to horizontaland vertical deflection amplifiers 64 and 66, respectively. Thehorizontal and vertical amplifiers 64 and 66 are of the push-pullparaphase amplifier type, well known in the art; each amplifierproducing at its output voltages in push-pull relationship forapplication to the deflection controls or plates of a cathode ray tube.The horizontal deflection amplifier 64 has its output connected acrossthe horizontal deflection plates 68 and 70 of the cathode ray tube 10;and the vertical deflection amplifier 66 has its output connected inpush-pull to the vertical deflection plates 72 and 74 of the cathode raytube 10. Since the apparatus of the present invention is particularlyapplicable for producing rotating time base displays whose time basesare a' relatively long time duration, say onethirtieth of a second, thehorizontal and vertical deflection amplifiers V64 and 66 are designed tohave a relatively good low frequency response.

The operation of the' apparatus for producing the rotating'` time basedisplay will now be described. The output saw-tooth wave 14 of thesaw-tooth generator 12 is fed to the input of the phase-splitter 16. Theamplified sawtooth voltages at the outputs of the phase splitter 16 areapplied in push-pull to the grids of the cathode followers 18 and 20',connected in push-pull circuit. The inputs to the grids of the cathodefollowers 155 and 20 are shown as waveforms 76 and 78, which are' equalin magnitude but of opposite polarity.

In order Ato produce a rotating time base display on the cathode raytube 10 inthe form of a trace of a diameter line'ro'tat'in'g about itscenter, it is necessary to provide one set of deflection plates withsaw-tooth voltages whose peak-to-peakamplitudes vary as a sine function,and the other set of deflection plates with a set of saw-tooth v'oltageswhose peak-to-peak amplitudes vary as a cosine function. To thisend,.the resistor 4t) isrotated substantially in the plane of theinsulating material 42 about its center 52, by any's'uitable means (notshown). The voltage picked offby any on'e brush, such as the brush 54',in slideable contact with the circle of rotation' 62 on the resist-ance40,-v will be a voltage whose amplitude varies sinusoidally from amixinium o'f one polarity, through 4 zero, to a maximum of the oppositepolarity. The voltage deivd at the ct't' briisl 56 will va'y iii asiila' manner but will be related to the voltage at the brush 54 in aquadrature relationship. In other words, when the brush 54 is adjacentone end of the resistor 40 a positive-going saw-toothvoltage of maximumamplitude will be derived. After the resistance has rotated this voltagewill be reduced in amplitude to zero. Rotating the resistance 90 more inthe same direction will result in a negative-going Asaw-tooth voltageatthe brush 54,` and rotating the resistance another 90" will result inthe voltage at the brush 54- ietu'rning to zero.

It is important that no D. C. voltage appear across the resistor 40. Forexample, a D. C. voltmeter connected across the brushes 44 and 48 shouldread zero at all times. if this were not so, a low frequency sinusoidalvoltage would be picked off by the brushes 54 to 60, as the resistor 40rotates, and provide the deflection electrodes 68 to 74 with voltagesthat willJ cause `the trace 80 on the face of the cathode ray tube 10 towobble instead of rotating` about its center.

i ln the preferred embodiment of the present invention, the voltagespicked off by` the brushes 54 and 56 of the sine-cosine potentiometer 38are applied to thedeflection plates of the cathode ray tube 10' throughthe horizontal and vertical deflection amplifiers 64 and 66. However,the horizontal and vertical amplifiers 64 and 66 could be eliminated ifenough drive is available at the brushes 54 to 60 of the potentiometer38. in the latter embodiment, shown in Fig. 2, the brushes 54, 56, 5 8and 60 of the sine-cosine potentiometer are connected directly to thedeflection electrodes 68, 74, 72 and 70, respectively, ofthe cathode raytube 10.

Thus, there has been s hownv and described in accordance with theobjects of the present invention, highly improved apparatus forproducing a rotating time base display on a cathode ray tube. Theapparatus of the present invention uses fewer components foraccomplishing the same purpose as prior art apparatus, and provides aunique arrangement for maintaining a zero D. C. potential across theresistor of the sine-cosine potentiometer at all times. Because of thislatter feature, the apparatus of the present invention is particularlyadaptable for use with relatively low frequency saw-tooth voltages andthe lo,I frequency-response deflection amplifiers used therewith.

What is claimed is:

l'. Apparatus for producing a rotating time base display on a cathoderay tube having deflection means, said apparatus comprising means toproduce an alternating voltage, phase-splitting means connected to saidalternating voltage producing means to produce push-pull alternatingoutput voltages, a push-pull cathode follower circuit comprising a pairof vacuum tubes each having an anode, a grid and a cathode, asine-cosine potentiometer having a rotatable resistor, means connectingsaid rotatable' resistor between the cathodes of said pair of vacuumtubes, a plurality of bmshes in slideable contact with said resistor,means coupled to said grids to apply saidV pushpull alternating outputvoltages thereto, and means connecting said brushes to said deflectionmeans of said cathode ray tube.

2. Apparatus forv producing a rotating time base display on aV cathoderay tube having deflection means, said apparatus comprising `means toproduce an alternating voltage, phase-splitting means connected to saidalternating' voltage producing means to produce push-pull alternatingoutput voltages, a push-pull cathode follower circuit comprising a p'airof vacuum tubes each having an anode, a grid and a cathode, asine-cosine potentiometer having a resistor rotatable in a circle ofrotation, means connecting said rotatable resistor between the cathodesof said pair of vacuum tubes, a plurality of brushes in slideableContact withsaidl resistor, means coupled to said grids: to apply saidpush-pull alternatingoutput voltages thereto, and means connecting saidbrushes to said deflection means of said cathode ray tube, said means toproduce an alternating voltage comprising a saw-tooth generator.

3. Apparatus for producing a rotating time base display on a cathode raytube having deiiection means, said apparatus comprising means to producean alternating voltage, phase-splitting means connected to saidalternating voltage producing means to produce push-pull alternatingoutput voltages, a push-pull cathode follower circuit comprising a pairof vacuum tubes each having an anode, a grid and a cathode, asine-cosine potentiometer having a resistor rotatable in a circle ofrotation, means connecting said rotatable resistor between the cathodesof said pair of vacuum tubes, a plurality of brushes in slideablecontact with said resistor, means coupled to said grids to apply saidpush-pull alternating output voltages thereto, and means connecting saidbrushes to said detlection means of said cathode ray tube, saidplurality of brushes comprising four brushes spaced 90 from each otheron said circle of rotation of said resistor.

4. Apparatus for producing a rotating time base display on a cathode raytube having deflection means, said apparatus comprising means to producean alternating voltage, phase-splitting means connected to saidalternating voltage producing means to produce push-pull alternatingoutput voltages, a push-pull cathode follower circuit comprising a pairof vacuum tubes each having an anode, a grid and a cathode, asine-cosine potentiometer having a resistor rotatable in a circle ofrotation, means n connecting said rotatable resistor between thecathodes of said pair of vacuum tubes, a plurality of brushes inslideable Contact with said resistor, means coupled to said grids toapply said push-pull alternating output voltages thereto, meansconnecting said brushes to said dellection means of said cathode raytube, said plurality of brushes comprising two brushes spaced 90 fromeach other on said circle of rotation of said resistor, and said meansconnecting said brushes to said deflection means including push-pullhorizontal and vertical deflection ampliliers connected between saidbrushes respectively and said cathode ray tube.

5. Apparatus for producing a rotating time base display on a cathode raytube having horizontal and vertical delection electrodes, said apparatuscomprising a saw-tooth generator, a phase-splitter connected to saidgenerator whereby to provide a push-pull output voltage, a cathodefollower circuit comprising two electron discharge devices each having agrid, and a cathode, means to couple said push-pull output voltage inpush-pull to said grids of said devices, a sine-cosine potentiometerhaving a resistor rotatable in a circle of rotation, means connectingsaid rotatable resistor between the cathodes of said devices, aplurality of brushes in slideable contact with said rotatable resistoron said circle of rotation, selected ones of said brushes beingconnected to selected ones of said horizontal and vertical electrodes.

6, Apparatus for producing a rotating time base display on a cathode raytube having horizontal and vertical dellection electrodes, saidapparatus comprising a sawtooth generator, a phase-splitter connected tosaid generator whcreby to provide a push-pull output voltage, a cathodefollower circuit comprising two electron discharge devices each having agrid, and a cathode, means to couple said push-pull output voltage inpush-pull to said grids of said devices, a sine-cosine potentiometerhaving a resistor rotatable in a circle of rotation, means connectingsaid rotatable resistor between the cathodes or said devices, fourbrushes in slideable contact with said rotatable resistor spaced aparton said circle of rotation, and means connecting pairs of alternatelyspaced brushes to said horizontal and vertical deflection electrodes,respectively.

7. Apparatus for producing a rotating time base display on a cathode raytube having horizontal and vertical delection electrodes, said apparatuscomprising a saw-tooth generator, a phase-splitter connected to saidgenerator whereby to provide a push-pull output voltage, a cathodefollower circuit comprising two electron discharge devices each having agrid, and a cathode, means to couple said push-pull output voltage inpush-pull to said grids to said devices, a sine-cosine potentiometerhaving a resistor rotatable in a circle or" rotation, means connectingsaid rotatable resistor between the cathodes of said devices, ahorizontal and a vertical del'lection amplifier, a pair of brushes inslideable contact with said rotatable resistor each spaced 90 withrespect to the other on said circle of rotation, means connecting saidhorizontal amplier between one of said brushes and said horizontaldeflection electrodes, and means connecting said vertical amplierbetween the other of said brushes and said vertical dellectionelectrodes.

References Cited in the file of this patent UNITED STATES PATENTS2,411,030 De Ryder Nov. 12, 1946 2,474,177 Wild June 21, 1949 2,575,477Weimer Nov. 20, 1951 2,637,026 Koehler a- Apr. 28, 1953 2,660,691Bertram Nov. 24, 1953

